Table of Contents

Overview

California’s Sea Level Is Rising

And It’s Costing Over $6 Billion

The sea level off California’s coast is up to 6 inches higher than it was in 1950.1 This increase is mostly due to ice melting into the ocean2 and thermal expansion,3 and it’s causing major issues. Solutions in California can be complicated because the state has more coastal residents than any other in the U.S.4 as well as habitats and billions of dollars worth of real estate at risk. The state is planning over $6 billion in sea level rise solutions, which include seawall improvements, flood mitigation for major roads, and wetland restoration and fortification.

Sea level rise is speeding up

The sea level around San Francisco, California, has risen by 6 inches since 1950. Its speed of rise has accelerated over the last ten years and it’s now rising by about 1 inch every 10 years.1 Scientists know this because the sea level is measured every 6 minutes using equipment like satellites, floating buoys off the coast, and tidal gauges to accurately measure the local sea level as it accelerates and changes.6

Created with Highcharts 6.2.0

Sea level measurement from San Francisco area tide gauge since 1950

Causes & Complications

Why Are Sea Levels Rising?

While there are four main causes of sea level rise in California, ice melt2 and thermal expansion3 are the largest contributors. Because the rate of ice melt has been increasing significantly since 1992 and the ocean is getting warmer and expanding, California is particularly vulnerable to an increased rate of sea level rise in the future.2Click here to learn more about these causes.

How Ice Melt Increases Sea Level Rise

How Thermal Expansion Increases Sea Level Rise

El Niño can worsen West Coast flooding

In California, sea level rise and flooding can be impacted by El Niño weather events, which cause warmer ocean temperatures in the Pacific Ocean off the West Coast.7 Because water expands as it warms, El Niño events can raise coastal sea levels for several months.8 An El Niño also pushes the southern jet stream further south, which increases rainfall in California and causes more frequent and severe floods, landslides, and coastal erosion.9 El Niño’s impacts are particularly strong in late winter, and bring the most rain to Southern California.9

Most flooding happens in the winter

The highest tides in California occur during winter storms that push more water to the coast, raising high tides even higher. Combined with an increased gravitational pull from the moon, and the increased water levels caused by El Niño, tides in places like San Francisco are typically over a foot higher than normal high tides.1 Add that to the 6 inches of sea level rise since 1950 and you end up with flooding even on sunny days.

Solutions aren’t simple

Solutions can be complicated in California because the state is home to the largest amount of coastal residents in the U.S., with over 25 million people living near the sea.4 Over $100 billion worth of property along the California coast and vast natural ecosystems are at risk.10 Sea levels are already intruding into existing wetlands, and with current urban development in California, there is no place for these wetlands to travel inland in order to survive.11 In addition, the state faces a time clock, with coastal communities already experiencing major flood events,12 and two thirds of the beaches in Southern California on track to disappear.13

Forecast

What's the Future of Sea Level Rise?

In the last decade, the speed at which California’s sea level is rising has increased, and is now rising by as much as 1 inch every 10 years. Around San Francisco, it took around 39 years for the sea level to rise around 6 inches.1 Scientists now forecast that in just the next 16 years, the sea level will have risen by another 6 inches.14

Scientists are not certain how fast the ocean will warm and ice will melt. They expect water levels to continue to rise faster, but are not sure just how fast. Therefore scientists from the National Oceanic and Atmospheric Administration (NOAA) and the US Army Corps of Engineers (USACE) have made predictions based on ranges from low to high.

Below you can see the range of the NOAA and USACE high and intermediate forecasts for various locations around California.15 Currently, the USACE high forecast, seen as the darkest red line, is the most likely projection.

San Diego

Created with Highcharts 6.2.0San Diego Sea Level Rise Forecasts

Flooding

Why Are Floods More Frequent?

When the ocean rises high enough, high tides cause flooding even on sunny days. Even though the sea level near San Diego, California, has only risen by less than an inch,10 tidal flooding has increased by 550% since 2000.16

How sea level rise affects California

Flooding even when there’s no rain

Drainage systems are designed to channel excess rainwater from the streets and drain it into the sea. But with the pressure from rising sea levels and higher tides, seawater can get pushed into these pipes and spill out into the streets. This causes flooding even on days without rain.

Drainage Under Normal Tidal Conditions

Drainage With High Tide / Sea Level Rise

Increased storm surge flooding

Unfortunately, slightly higher sea levels make hurricanes even more damaging. Just a few more inches of sea level rise allow a hurricane to push more water onto the land, even if the hurricane itself doesn’t make landfall.

Hurricane Marie, 2014

Higher sea levels create a higher launching point for storm surge. These small changes in sea level rise are enough to turn what were 100-year storm surges into much more frequent events. In fact, in a third of 55 coastal sites studied throughout the US, 100-year storm surges will be 10-year or more frequent events by 2050.18

This means that in many coastal cities, if you bought a house with a 30-year mortgage today, by the time you paid off your mortgage you could be experiencing extreme 100-year storm surges ten times more frequently due to sea level rise alone. This does not include the added risk of more intense storms resulting from warmer water and a warmer atmosphere, which could further increase storm surge damage.

In 2014, Hurricane Marie struck off the shores of California, bringing sustained winds of over 160 mph and 15 foot swells that caused nearly $20 million in damage.19 Without sea level rise, Hurricane Marie’s swells would have been much lower.

Hurricane Marie, 2014

Costs

What's at Risk in California?

There’s a lot at risk from sea level rise and flooding in California. Higher seas off Southern California are expected to increase coastal erosion, causing breaks in seaside cliffs and changes to the state’s coastline.20 Sea level rise also threatens many popular California surf spots, as higher tides affect the way that waves break.21 Wetlands are at risk, with current high projections indicating that the state will lose the majority of its coastal wetlands within 100 years.10 Higher sea levels also increase the risk of saltwater getting into the state’s freshwater supplies, which puts California’s drinking water in danger.22

COASTAL WETLANDS

BEACHES

Rising seas increase the speed of beach erosion, pulling more sand from the beach into sea. Replacing the sand is possible, but expensive.

DRINKING WATER

The ocean is salty, and as it rises higher, that salty water sometimes will mix with drinking water, ruining water wells.

California is spending over $6 billion on solutions

Some cities have sufficient resources to deal with this problem while others do not. California will need solutions at the individual, local, state, and federal levels to protect its coastal communities.

San Francisco

San Francisco is planning a $5 billion infrastructure improvement project for the city’s seawall, which will increase protection against sea level rise and flooding.23

California

The $1.5 billion improvement plan for California State Route 37 will include solutions that protect against sea level rise and flooding.24

San Elijo Lagoon

A $120 million project at San Elijo Lagoon includes dredging and the creation of dikes to offer refuge to wildlife.25